As coming into this information era, there has been in an increased demand for organic compounds capable of absorbing light in the ultra violet to the infrared regions. As can be seen in filter materials, the uses of such compounds have been expanded from the fields, where their properties of absorbing light to shield it are used, to others such as information recordings and solar energy generations, where light energy is positively used via the organic compounds.
The properties to be possessed by organic compounds applied to the above-identified fields can be listed as follows; a satisfactory light-absorption property and light tolerance in the ultra violet to the infrared regions, an improved solubility in solvents, and an exertion of thermal property depending on uses. Representative examples of organic compounds proposed so far include anthraquinone dyes phthalocyanine dyes, cyanine dyes as methane dyes, and styryl dyes (see, for example, Japanese Patent Kokai Nos. 116611/89, 2002-202592, 2003-167343, 58961/99, and 2003-231359), and among which anthraquinone dyes are said to be defective in light absorption property and phthalocyanine dyes are said to be defective in both light absorption property and solubility in solvents. Methine dyes have been tried to improve their light absorption property and solubility by the introduction of substituents and the dimerization of dye skeleton, however, even now there are only a few that fulfil functions such as light tolerance and thermal property, as well as light absorption property and solubility.
As coming into this multi-media age, optical recording media such as CD-Rs, DVD-Rs, recordable blue-laser disks (abbreviated as “BD-Rs”, herein after), and HD DVD-Rs are highlighted in the field of information recordings. The optical recording media can be roughly classified into light-magnetic recording media, phase-change recording media, chalcogen oxide recording media, and organic optical recording media.
Among which, organic optical recording media are usually prepared by dissolving methine dyes in organic solvents such as 2,2,3,3-tetra fluoro-1-propanol (abbreviated as “TFP”, herein after), applying the solutions over polycarbonate substrates, drying the resulting substrates to form recording layers, and sequentially attaching thereunto reflection layers of metals such as gold, silver, or copper and protection layers of ultra violet ray hardening resins. Organic optical recording media have the defects that the recording layers are susceptible to change due to environmental light such as reading light and natural light, but have the merits that they can be prepared at a lesser cost because recording layers can be formed by directly applying methine dyes, as light-absorption materials, in a solution form.
What is urgently required in organic optical recording media is to more increase their recording intensity and information-recording speed to meet this multi-media age. For such high density growth, it has been promoted to shorten the wavelength of light used for writing and reading. To attain a more increased high speed, more sensitive methine dyes should be desirably used, however, it tends to increase jitters to the time direction of reproduction signals and to lower light stability (light tolerance). To meet a further improvement in such high speed trend in the future, mere application of conventionally known methine dyes to such optical recording media is becoming to be incapable of attaining sufficient sensitivity, jitter, and light stability effective to record information at a relatively high speed.